The present invention relates to a control valve for proper control of the hydraulic pressure to be discharged from a hydraulic pressure source to a hydraulic device such as a hydraulic-actuated clutch or the like, and in particular to a control valve wherein the hook and the boom of a crane are arranged in the hydraulic circuit of a two-drum type hydraulic-actuated winch to control the actuation thereof, thus actuating a hoisting-up clutch, a hoisting-down clutch, and a brake in actuation in a proper manner.
A conventional control valve of this category is of such a construction that the control valve is directly actuated by a control lever for applying and releasing the hydraulic pressure from a hydraulic pressure source to a hydraulic device. Therefore, a series of such defects that an operator cannot properly sense out at all the hydraulic pressure thus fed to the hydraulic device, and that proper judgment cannot be passed with regard to the state of the hydraulic device in actuation are involved therein naturally enough.